Exhaust units in internal-combustion engines as used today comprise a set of pipes which can be jointed to exhaust ports of the engine, which in turn converge into a single end conduit leading to a catalyzer or, in sports cars, directly to a silencer.
Particularly in high-performance engines, such as used in sports and competitions, it is important to design the exhaust system appropriately, with special regard to the dynamics and resistance of the gas flow, since these factors may considerably affect the engine's performance.
With reference to this, it has been found expedient that the exhaust gases from the different cylinders follow paths of substantially equal lengths, and that the pipes fit into the terminal exhaust tube with smooth angles, in order to avoid local resistances to the gas flow. In general, the aim is to favor the confluence of the gases into the terminal conduit, while avoiding that the gases coming from different cylinders may cross and hinder one another.
Exhaust systems designed to optimize the engine's performance according to the above criteria are generally quite bulky and, particularly in view of their monolithic structure, difficult to integrate within the vehicle, which is normally designed for standard exhausts. Consequently, their installation involves disassembling the engine, which is a difficult and time-consuming job.
Moreover, the small dimensional variations which are unavoidable among different frames even if belonging to the same model, and due to tolerances in manufacture and assembly, make it necessary that such exhaust systems have a certain degree of adaptability in assembly.
This requirement has not been satisfactorily met until now, on the one hand, due to the difficulty of inserting flexible components in the pipes because of their high operating temperatures, which do not allow synthetic materials to be used, and, on the other hand, due to the requirement of maintaining a perfect seal in the joints, in order to avoid gas leaks in intermediate areas of the unit.